Self-adjusting clutch or brake

ABSTRACT

The armature ring of a magnetic friction brake or clutch is supported on a rotary hub through the medium of a plurality of angularly spaced leaf springs extending along secants of the armature, riveted at opposite ends to the armature and hub, and stressed to bias the armature axially away from its coating magnet face. Pins rigid with the armature project loosely into holes in the hub and carry split resilient rings which constitute frictionally held stops movable between axially spaced abutments on the hub, one abutment acting when the brake is energized to shift the ring along the pin a distance corresponding to the wearing off of the armature face in previous brake applications. The other abutment coacts with the stop ring to determine the extent of separation of the armature from its magnet when the latter is deactivated and thus determine the width of the idle air gap between the rings.

United States Patent [72] Inventor Edward R. Kroeger Beloit, Wis. [21]Appl. No. 61,193 [22] Filed Aug. 5, 1970 [45] Patented Nov. 30, 1971[73] Assignee Warner Electric Brake & Clutch Company Beloit, Wis.

[54] SELF-ADJUSTING CLUTCH OR BRAKE 14 Claims, 13 Drawing Figs.

52 0.5. Ci 192/18 B, l88/71.8, 188/196 P, 192/84 A, 192/111 A [51]1nt.Cl. ..Fl6d 13/75, F16d 65/52 [50] Field olSeareh 192/18 B, 84A, 111A; 188/713, 196P [56] References Cited UNITED STATES PATENTS 2,705,0583/1955 Harter 188/196 P X 3,086,634 4/1963 Reed 192/111 A 3,255,8466/1966 Livezey 192/111 A X 3,421,604 H1969 Hobbs 192/1 11 A X 3,485,33012/1969 Reiff 192/111 A X FOREIGN PATENTS 966,888 8/1964 Great Britain192/111 A Primary Examiner-Allan D. Herrmann Attorney-Wolfe, Hubbard,Leydig, Voit & Osann ABSTRACT: The armature ring of a magnetic frictionbrake or clutch is supported on a rotaryhub through the medium of aplurality of angularly spaced leaf springs extending along secants ofthe armature, riveted at opposite ends to the armature and hub, andstressed to bias the armature axially away from its coating magnet face.Pins rigid with the armature project loosely into holes in the hub andcarry split resilient rings which constitute frictionally held stopsmovable between axially spaced abutments on the hub, one abutment actingwhen the brake is energized'to shift the ring along the pin a distancecorresponding to the wearing off of the armature face in previous brakeapplications. The other abutment coacts with the stop ring to determinethe extent of separation of the armature from its magnet when the latterisdeactivated and thus determine the width of the idle air gap betweenthe rings.

SELF-ADJUSTING CLUTCH OR BRAKE BACKGROUND OF THE INVENTION Thisinvention relates to magnetic friction clutches and brakes in whichrelatively rotatable rings of magnetic material are drawn into axialgripping engagement by flux threading a toroidal flux path defined bythe rings and has more particular reference to such torque-producingcouplings which are equipped with one or more devices for sensing wearat the friction faces and operating, as an incident to successiveattractions and releases of the coupling rings, to automatically adjustthe axial position of one of the rings and maintain an air gap of narrowand approximately constant width after each deenergization of thecoupling.

In such wear-adjusting devices as disclosed, for example, in US. Pat.No. 2,705,058, a frictionally supported stop carried by the axiallymovable magnetic ring moves against one abutment when the coupling isenergized and slips relative to the ring by an amount determined by theexisting amount of wear. When the coupling is deenergized, the ring andstop are biased away from the coacting ring and against a secondabutment which limits the separation and determines the width of theresulting gap between the ring faces of the idle coupling.

In prior devices of this character, the pin supporting the frictionstops transmits the coupling torque thus imposing on the pin a frictionload which makes it difficult to maintain an idle gap as small asdesired or to insure uniformity of the gap width. In addition, themagnet ring and the adjusting devices are usually supported through aspline coupling which inherently incorporates angular backlash thatcannot be tolerated in many modern motion-control installations.

SUMMARY OF THE INVENTION The primary aim of the present invention is toeliminate backlash in magnetic couplings of the above character whileavoiding the transmission of the coupling torque through the parts ofthe automatic gap-adjusting devices. This is accomplished by supportingthe axially movable magnetic ring for free axial floating through themedium of a plurality of angularly spaced leaf springs which extendgenerally tangentially of the ring and are stressed endwise to transmitthe coupling torque without imposing any torque or friction load on theparts of the gap-adjusting devices.

Another object is to mount the stop controlling pins of thegap-adjusting devices for free endwise movement with the magnetic ringso that by lateral prestressing of the leaf springs, the latter areutilized to provide the necessary ring separating force and to coactwith the friction stops to maintain between the coupling rings an idleair gap which is precisely uniform and substantially narrower, forexample, only a few thousandths of an inch, than has been possible withthe similar wear-adjusting devices of the prior art.

The invention also resides in the novel mounting of the gap controllingpins and the construction of the stop limiting abutments.

Another object is to provide a novel hub construction for enabling botharmatures of a clutch-brake coupling to be mounted thereon through themedium of pairs of leaf springs of the above character while providingoptimum axial compactness of the assembly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an end view of a magneticring and its supporting hub of a friction coupling embodying the novelfeatures of the present invention.

FIG. 2 is a section taken along the line 2-2 of FIG 1 with the couplingdeenergized.

FIG. 3 is a similar section with the coupling engaged.

Fl 3. 4, and 6 are sections taken along the lines 44, 5 5 and 6-6 ofFlG.2.

FIG. 7 is a perspective view showing a subassembly of the magnet ringand its supporting leaf springs.

FIG. 8 is an exploded cross-sectional view of the magnetic ring and theassociated parts for supporting the same.

FIGS. 9 and 10 are fragmentary views similar to FIG. 2, showingmodifications in the mounting of the gap controlling stop.

FIG. 11 is a fragmentary section similar to FIG. 2 of a combined clutchand brake incorporating the present invention, the section being takenalong the line 11-11 of FIG. 12.

FIG. 12 is a section taken along the line I2--I2 of FIG. I 1.

FIG. 13 is a section taken along the line 13-13 of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For the sake of simplicity, theinvention is shown in FIGS. 1 to 8 of the drawings incorporated in anelectromagnetic friction brake comprising an annular ring 10 of magneticiron fixed as by welds to a plate 10a which in turn is secured as byscrews 10b to a stationary support 11 and a rotatably mounted armatureor driving ring 12 forming with the magnet ring a toroidal flux circuit13 and adapted to be drawn into axial gripping engagement with the faceof the magnet ring upon energization of a multiple turn coil 14 disposedbetween the concentric pole pieces of the magnet. The magnet ring is ofU- shaped cross section and its pole pieces are spanned radially by anannulus 15 of weanresistant material whose axial facing surface is flushwith the pole faces 16 of the magnet ring. The opposed face 17 of thearmature ring is substantially flat and overlaps the inner and outerpole faces of the magnet ring to complete the flux circuit. As iscustomary, outwardly opening slots 18 are formed in and extend radiallyacross the major width of the armature face 17 to receive particleswearing off from the engaging faces in service use and throw suchparticles out of the way. The armature is mounted on a disklike hub 20which is secured as by set screws 21 on a shaft 22 whose motion is to becontrolled by the brake. The shaft is journaled and axially fixed in thesupport 11 and projects axially through the magnet and armature ringsand into the hub.

As set forth above, the invention contemplates transmission of thebraking torque to the hub and supporting the armature ring for freeaxial floating through the use of a plurality of angularly spaced andgenerally tangentially extending leaf springs 23 which are prestressedlaterally to provide the force needed for separating the armature fromthe magnet face when the brake is deenergized and enable an equal numberof wear-sensing devices 25 to act in limiting the armature separation soas to establish an idle gap 26 when the magnet is deenergized and thebrake released. By virtue of the present invention, the gap may beextremely narrow, for example 0.003 to 0.007 of an inch, and will alwaysbe of precisely the same width after each release of the brake.

Three substantially flat and straight leafs of ordinary spring steel arepreferably employed and disposed between the flat back 24 of thearmature ring and the opposed inner end face 27 of the hub. Herein, theends 28 of the three springs are equally spaced around and secured flatagainst the back of the armature and extend from these points around thearmature in the same direction and along secants of the armature as bestshown in FIGS. 4 and 7. The opposite ends 29 are similarly secured tothe face 27 of the hub. While the spring ends may be attached in otherways, deforming the leafs or straining the metal thereof is avoided byemploying rivets 30 and 31 extending through holes 32 and 33 in thespring ends 29 and 28 respectively. The shank of each rivet 30 extendsthrough a hole 34 in the hub with its peened over head 35 exposedthrough one of the armature slots 18 which is wide enough to accommodatethe riveting tool.

An important feature of the invention is the formation of the rivets 31from shanks comprising necked down end portions of cylindrical pins 36which constitute parts of the three wear-adjusting devices 25 abovereferred to. Each pin shank is projected through the hole 33 (FIG. 8) ina spring end 28 and an aligned hole 37 in the armature. Through adepression 38 in the armature face 17, the end of the shank 31 isaccessible for peening over of the metal to form the rivet head 39 withthe spring end clamped rigidly against a shoulder 42 at the inner end ofthe pin shank.

It will be apparent that the armature is supported from the rotating hub20 solely by the leaf springs 23 which, by lateral flexing along thecoupling axis, provide for free axial floating of the ring toward andaway from the magnet face. For the same reason, all of the retardingtorque is transmitted endwise through the leaf springs which are placedunder tension when the brake is applied with the shaft 22 rotating inone direction and under compression in the other direction of rotation.All looseness or angular backlash in the coupling is thus eliminated. Ofcourse, the springs are flexible enough to provide the desired freeaxial floating of the armature and, according to the size and capacityof the coupling, are made wide and thick enough to avoid bucklingintermediate their riveted ends 28 and 29 when the direction of thetransmitted torque is such as to place the springs under endwisecompression. The spring ends 28 and 29 are relatively large in area andclamped against the fiat surfaces 24 and 27 on the armature back and thehub so that the danger of buckling of the springs is effectuallyminimized.

In the present instance, the leaf springs, in addition to supporting thearmature ring without backlash, are utilized, as will appear presently,to perform a new function in combination with the wear-adjusting devices25, that function being to force the armature ring away from the magnetwhen the latter is deenergized to release the brake or clutch as thecase may be. For this purpose, the springs are bent initially as shownin FIG. 8 or in the course of the final assembly of the coupling partsso that each spring is prestressed in a direction to provide an axiallydirected force of proper magnitude coritinuously biasing the armatureaway from the magnet and thus forcing separation of the two when themagnet is deenergized.

The wear-adjusting devices 25 above referred to for maintaining aprecisely constant and narrow width of the idle gap 26 correspond innumber to the leaf springs 23 and are advantageously located at thespring ends 28 because the rivets 31 for fixing these ends to thearmature also serve to support the cylindrical pins 36 of such devices.In the final assembly (FIGS. 1 and 2), these pins project into andsubstantially through parallel holes 43 in the hub spaced around thecoupling axis to receive the projecting pins 36 of the armature assembly(FIG. 7), the holes being slightly larger in diameter than the pins soas to provide continuous clearance 44 around the latter.

Friction stops in the form of radially expansible or contractable rings41 of resilient material are interposed between external surfaces of thepins 36 and internal surfaces of the holes 43 and sized and stressed togrip one of such surfaces frictionally and resist axial shifting of therings axially of the pins with a total force which is somewhat greaterthan the force exerted by the leaf springs 23 in biasing the armatureaway from the magnet face and toward the hub. This resisting force isvery small as compared with the magnetic attractive force that draws thearmature ring against the magnet face 16 when the coil 14 is energizedto apply the brake.

The rings 41 may be composed of various resilient materials and take theform of a continuous circle or polygon of firm rubber or plastic or,preferably, as in the present instance, the ring may be split, composedof spring wire, and stressed to expand during insertion of a pin 36therethrough and then contract (See FIGS. 1 and 9) with the desiredgripping pressure around the exterior of the ring. As an alternative andas shown in FIG. 10, the ring may be stressed to expand and similarlygrip the internal wall defining the hole 43. In each instance, thediameter of the resilient material of the rings is somewhat greater thanthe radial clearance 44 between the opposed pin and hole walls so thatone peripheral edge portion of the rings projects radially in betweenopposed and axially facing walls 45 and 46 of a groove or slot formed inthe hub around the pin holes (FIGS. 1 and 9) or in and around the pin(FIG. These walls are axially spaced-apart a distance greater thandiameter of the ring wire by an amount precisely equal to the width ofthe gap 26 which it is desired to maintain between the magnet andarmature faces when the brake is released (FIG. l).

In the form shown in FIGS. 1 to 6, the wall 45 constitutes an abutmentfor controlling the sliding of the split ring along its pin 36 as thearmature, whose face 17 may have worn away in previous brakeengagements, comes against the magnet face 16 when the brake is appliedas shown in FIG. 2. Thus, this abutment coacts with the split frictionring during engagement of the brake to sense the wear which may haveoccurred in previous brake applications, the ring being shifted alongits pin and away from the armature in exact accordance with the amountof such axial wear.

The other abutment wall 46 is disposed in the path of retraction of thesplit ring 41 in its newly adjusted position and engages the ring asshown in FIG. 1 to limit the extent of separation of the armature fromthe magnet under the action of the leaf springs 23. Preferably, the stoprings 41 are, when the armature is new and its face unworn, adjusted topositions along the pins 36 so as to be in engagement with the abutment46 as shown in FIG. 1 when the gap 26 is of the desired width.

It is apparent from the foregoing that the frictionally held stop rings41 coact with the abutments 45 and 46 respectively in the movements ofthe armature toward and away from the magnet face so as to senseexisting wear at the magnet and armature faces 16 and 17 and limit theretraction of the armature by the leaf springs 23 to compensate for suchwear and always maintain an idle gap 26 of precisely uniform and verynarrow width. Thus, the mechanical time delay incident to fullengagement of friction coupling will be reduced to a minimum due to themaintained narrowness of the gap 26, and the time for developing thefull torque of the clutch or brake will be extremely uniform under allconditions of service use. This, together with the antibacklash mountingabove described, greatly extends the usefulness of couplings of thepresent character.

Another important feature of the invention is the construction of theabutments 45 and 46 in order-to facilitate ease of assembly and achieveoptimum overall axial compactness of the supporting hub. To this end,outwardly opening and narrow slots 48 (FIGS. 1 to 3) disposed in planesnormal to the coupling axis are cut in angularly spaced portions 50 ofthe outer end of the hub 20 to provide pairs of opposed parallel wallswhose inner end portions define the properly spaced abutments for eachof the stop rings 41. In the hub construction shown in FIGS. 1 to 6, thepin holes 43 extend through the hub portions 50 and areas 51 of the hubadjacent one side of these portions are cut away and depressed toreceive the heads of the rivets 30 which heads are disposed below theplane of the slots 48. Thus the latter and the abutments may be formedin a simple sawing operation. Since the slots thus formed open outwardlyor radially relative to the parts 50 of the hub, the split rings 41 maybe inserted edgewise into the slots and easily centered relative to thepin holes 43.

In assembling the coupling, the leaf springs are riveted to the back ofthe armature and to the ends of the pins 36 to form the subassemblyshown in FIG. 7. Then, after inserting the stop rings 41 edgewise intothe slots 48 and locating the same in axial alignment with the pin holes43, the subassembly is placed adjacent the hub with the beveled freeends 52 of the pins aligned with the holes, such ends guiding the entryof the pins through the stop rings as the hub and subassembly arepressed together. The holes 32 in the spring ends 29 are thus broughtinto alignment with the hub holes 34 permitting insertion of the rivets30 and peening thereof to form the heads 35 and thus secure the springends to the hub. If desired, the proper prestressing of the leaf springto provide the desired armature separating force may be effected afterthe final assembly as by holding the armature face against the magnetand separating the hub from the armature by a small amount to producethe proper prestress.

When the invention is incorporated in a coupling of larger size it maybe desirable to form the abutments 45 and 46 as the opposite walls of agroove 53 formed as with a suitable single point boring tool. Such amodification is shown in FIG. 9, the exterior of the hub being leftuninterrupted and cylindrical.

Instead of forming the abutments and 46 in the hub. these may be formedon the pin 36 as in the modification shown in FIG. 10. For thisarrangement, the friction necessary to hold the stop on the pin isachieved by construction of the ring to expand against the cylindricalinterior of the hole wall instead of contracting around the pin as inthe preferred form first described.

The leaf 'spring armature mountingand the automatic air gap maintainingdevices may be used in magnetic friction clutches as well as in brakesas above described and are especially adaptable for use in clutch-brakecombinations as illustrated in FIGS. 11 to 13 so as to achieve overallaxial compactness by mounting of the armatures and $6 of a clutch 57 anda brake 58 on a disk 59 in a novel manner to provide optimum overallaxial compactness of the combined couplings. As before, the flatarmature ring 56 of the brake is disposed adjacent the pole faces of amagnet ring 63 fixed to a suitable support 64 and adapted when its coil63a is energized to draw the armature into axial gripping engagementwith its friction face 63b and develop a friction torque which istransmitted through the armature and a leaf spring coupling as describedabove to a driven shaft 62 journaled in suitable bearings (not shown)which hold the hub axially fixed.

The clutch 57 shown is of the stationary field type having a U-shapedmagnet ring fixed to a support 600 and concentric pole pieces separatedby a narrow radial gap 65 from the corresponding concentric pole piecesof a rotor 66 having an annulus 67 of wear-resistant material fixedbetween and flush with the pole faces 68 of the rotor. The inner polepiece of the rotor is pressed on a flange 69 on a hub 70 suitably fixedagainst a shoulder 71 on a driving shaft 72. The latter is journaled insuitable bearings 72a mounted in the support 64 and maintaining therotor axially fixed and concentric with the clutch axis. The armatures55 and 56 are disposed on opposite sides of the disk 59 which isintegral with a central hub 73 suitably fixed onto the inner end of andagainst a shoulder 96 on the driven shaft 62.

As in the brake first described, the clutch armature 55 is supportedthrough flat and secantially extending leaf springs 74 each having oneend 85 secured to the armature 55 by a rivet 75 formed by the end of apin 76 which projects loosely into one of three holes 77 equally spacedaround the periphery of the disk 59. The armature 56 of the brake issimilarly supported by axially flexible leaf springs 78 extending alongsecants of the armature and disposed between the hub disk and the flatback of the armature. One end of each of these springs is secured to theback of the armature 56 by a rivet 87 (FIG. 13) formed by one endportion of a pin 88 which projects loosely into one of three holes 89equally spaced around the periphery of the disk 59.

The clutch and brake leaf springs 74 and 78 are arranged in alternatingrelation or staggered angularly around opposite sides of the disk 59 sothat the ends 80 and 81 of one pair of the springs 74 and 78 align witheach other as shown in FIG. 11 and with a hole 82 through the disk andreceive a common rivet 84 by which the overlapping spring ends and thedisk are secured together. By virtue of such staggering of the leafsprings of the sets supporting the clutch and brake armatures onopposite sides of the hub and securing one end of a spring of each setto opposite sides of the hub by a single rivet, the supporting disk 59may be of minimum axial thickness and the construction of the mountingfor the armatures correspondingly simplified.

As before, the pins 76 and 88 constitute parts of devices for sensingwearing off of the clutch and brake faces and limiting separation of thearmatures from the associated magnets upon deenergization of the latterso as to establish idle gaps 90 and 91 (FIG. 11). As shown in FIG. 13,these devices include split rings of spring wire 92 for the brake pins88 and 93 for the clutch pins 76. These rings are disposed in commonslots 94 which, by a sawing operation, may be cut across the fullarcuate width of radial arms 5911 on the disk 59. The opposed walls ofeach slot thus constitute the necessary abutments for coacting, as inthe brake first described, with two of the split rings 93 and 92 and thepins 76 and 88 of the clutch and brake wear adjusting devices to sensewear at the friction faces when each coupling is energized and thendetermine the extent of separation of the armature from the associatedmagnet face when the coupling magnet is deenergized to release thecoupling.

The leaf springs 78 of the brake are prestressed in the manner abovedescribed so as to continuously bias the armature toward the disk 59.The leaf springs 74 supporting the clutch armature 55 are similarlyprestressed so as to bias this armature away from the pole faces 68 ofthe rotor 66 when the coil 61 is deenergized.

It will be apparent from the foregoing that in the clutchbrake unit(FIGS. 11 to 13), the leaf springs 74 and 78 provide mountings free ofbacklash supporting the clutch and brake armatures for free axialfloating while directly transmitting the clutch and brake torques thuspermitting a constant clearance 98 to be maintained around each of thepins 76, 88. Thus, the latter are slidable freely in the holes 77 and 89so that the wear-sensing and gap-determining devices formed by the pins76 and 88, the split rings 93, 92, and the associated abutments formedby the walls of the slots 94 may act to establish the air gaps 90 and 91of minimum thickness and precise uniformity.

With the leaf springs 74 and 78 arranged in the staggered relation onopposite sides of the supporting disk as shown in FIG. 12, a minimumnumber of the rivets 84 are required to secure the disk ends of thesprings and the pins 76 and 88 may be disposed in a common plane asshown in FIG. 13. Optimum axial compactness is thus achieved in the diskand double leaf spring and armature assembly.

I claim:

1. A friction-type torque-producing coupling having, in combination,axially fixed and axially movable relatively rotatable first and secondrings of magnetic material adapted to be drawn into axial grippingengagement by magnetic flux threading a toroidal path through the rings,an axially fixed support member disposed adjacent said second ring onthe side thereof opposite the first ring and having a plurality of holestherein angularly spaced around and paralleling the coupling axis, pinsrigid with said second ring and projecting slidably into the respectiveholes, stop members disposed intermediate the ends of said holes andfrictionally gripping and slidable axially relative to a peripheralsurface on one of said members, pairs of opposed abutments disposed onopposite sides of each of said stop members, one being engageable withthe stop member upon axial engagement of said rings to shift the stopmember along said axis by an amount equal to the wear that has occurredat said ring faces, the other abutments engaging the stop member tolimit the extent of separation of the rings when the latter aredeenergized whereby to establish an air gap of constant width each timethe rings are deenergized, and means supporting said second ring fromsaid support member and transmitting the coupling torque comprising aplurality of leaf springs between said support member and second ringangularly spaced around and extending along secants of the ring, andmeans securing opposite ends of said springs to said support member andsaid second ring respectively whereby such ring is supported for freeaxial floating and for transmitting torque between said rings, saidsprings being stressed to flex laterally and bias said second ring awayfrom the first ring with a force which is less than the frictionalresistance holding the axial positions of said stop members.

2. A torque-producing device as defined in claim 1 in which said pinsare located at the ends of said springs which are secured to said secondring.

3. A torque-producing device as defined in claim 1 in which one end ofeach of said pins is formed with a projecting shank terminating at ashoulder, said shank constituting a rivet having a head clamping thering and spring end against the shoulder.

3. A torque-producing coupling as defined in claim 1 in which oppositeends of said leaf springs lie against and are riveted rigidly to saidsupport member and second ring respectively.

5. A torque-producing coupling as defined in claim 1 in which the endsof said pins constitute rivets securing the ends of said springs to saidsecond ring.

6. A torque-producing device as defined in claim 1 in which each of saidstop members comprises a radially yieldable stop ring of resilientmaterial having one peripheral edge disposed between and axiallyengageable with said abutments and an opposite peripheral edge which, byvirtue of the radial resiliency of the ring, grips an opposed peripheralsurface to provide a predetermined friction gripping force resistingdisplacement of the stop ring relative to and along the axis of saidsecond magnetic ring.

7. A torque-producing coupling as defined in claim 1 in which the torqueresulting from gripping engagement of said magnetic rings, when thelatter are energized, is transmitted solely through endwise stressing ofsaid leaf springs and said second ring is supported at all times forfree sliding of said pins within the surrounding walls of said holes.

8. A torque-producing coupling as defined in claim 1 in which each ofsaid stop members is a ring of resilient material and said abutments arethe opposed walls of an annular groove surrounding the pins and widerthan the stop ring by the desired width of said constant gap when thecoupling is released.

9. A torque-producing device as defined in claim 8 in which said grooveis formed in said support as a slot opening outwardly in a plane normalto the coupling axis so as to pennit of edgewise insertion of the ringinto the slot and to a position of alignment with the axis of the pinhole.

10. A torque-producing coupling as defined in claim 9 in which the freeends of said pins are frustoconical to facilitate projection of the pinsthrough said stop rings after edgewise insertion of such rings in saidslots.

11. A torque-producing coupling as defined in claim 1 in which each ofsaid stop members is a ring of resilient material expanded radiallyagainst the wall of the surrounding hole and the associated abutmentsare the opposed axially facing walls of an annular groove in theassociated pin.

12. In a friction coupling having relatively rotatable first and secondrings of magnetic material adapted to be drawn into axial grippingengagement by magnetic flux threading a toroidal path through the rings,the combination of, a rotatable support, a plurality of leaf springsangularly spaced around and extending along secants of said first ringbetween said support and said ring, means securing opposite first andsecond ends of said springs to said support and the back of the ringrespectively, said springs being stressed to flex laterally and to biassaid first ring toward said support and away from said second ring upondeenergization of the rings, a plurality of angularly spaced pins rigidwith said first ring adjacent said first spring ends and projectingparallel to the first spring axis, parallel holes in said supportslidably receiving said pins. radially resilient stop rings encirclingand slidable along said pins within said holes but frictionally grippingthe pins to resist sliding along the pins with a force greater than saidbiasing force, and opposed axially facing abutments within each of saidholes disposed on opposite sides of the ring therein and spaced apart tocooperate with the respective stop rings and limit axial separation ofsaid first ring from the coacting magnetic ring so as to provide a gapof predetermined narrow width between the faces of said magnetic ringsupon deenergization of the latter.

13. In a magnetic friction clutch and brake of the character abovedescribed, a rotary hub, annular clutch armature concentric with the hubaxis and disposed at one end of said hub, a set of leaf springsangularly spaced around and extending along secants of said armaturebetween the latter and said hub, an annular brake armature disposedopposite the other end of said hub, a second set of leaf springsangularly spaced around and extending along secants of the brakearmature between the latter and said hub, the first and second leafsprings being staggered relative to each other around said armatures andhub with one end of each spring of one set overlapping an end of thecorrespondinglspring of the second set rivets each extending throughsaid ub and one pair of sal overlapping spring ends and securing thelatter to the hub, second rivets securing the other ends of said firstsprings to the back of the clutch armature, first parallel pins rigidwith and constituting extensions of said second rivets and projectingrigidly from such armature and into parallel holes in said hub, thirdrivets securing the other ends of said second springs to the back ofsaid brake armature, second parallel pins rigid with and constitutingextensions of said third rivets and projecting rigidly from sucharmature and into parallel holes in said hub, one of said first pins andone of said second pins being angularly spaced apart with one of saidfirst rivets disposed between such pins.

14. A magnetic armature ring mounting as defined in claim 13 in whichthe pins of the brake and clutch armatures project past each other andthe holes receiving such pins are disposed approximately in a commonplane of said hub.

1. A friction-type torque-producing coupling having, in combination, axially fixed and axially movable relatively rotatable first and second rings of magnetic material adapted to be drawn into axial gripping engagement by magnetic flux threading a toroidal path through the rings, an axially fixed support member disposed adjacent said second ring on the side thereof opposite the first ring and having a plurality of holes therein angularly spaced around and paralleling the coupling axis, pins rigid with said second ring and projecting slidably into the respective holes, stop members disposed intermediate the ends of said holes and frictionally gripping and slidable axially relative to a peripheral surface on one of said members, pairs of opposed abutments disposed on opposite sides of each of said stop members, one being engageable with the stop member upon axial engagement of said rings to shift the stop member along said axis by an amount equal to the wear that has occurred at said ring faces, the other abutments engaging the stop member to limit the extent of separation of the rings when the latter are deenergized whereby to establish an air gap of constant width each time the rings are deenergized, and means supporting said second ring from said support member and transmitting the coupling torque comprising a plurality of leaf springs between said support member and second ring angularly spaced around and extending along secants of the ring, and means securing opposite ends of said springs to said support member and said second ring respectively whereby such ring is supported for free axial floating and for transmitting torque between said rings, said springs being stressed to flex laterally and bias said second ring away from the first ring with a force which is less than the frictional resistance holding the axial positions of said stop members.
 2. A torque-producing device as defined in claim 1 in which said pins are located at the ends of said springs which are secured to said second ring.
 3. A torque-producing device as defined in claim 1 in which one end of each of said pins is formed with a projecting shank terminating at a shoulder, said shank constituting a rivet having a head clamping the ring and spring end against the shoulder.
 4. A torque-producing coupling as defined in claim 1 in which opposite ends of said leaf springs lie against and are riveted rigidly to said support member and second ring respectively.
 5. A torque-producing coupling as defined in claim 1 in which the ends of said pins constitute rivets securing the ends of said springs to said second ring.
 6. A torque-producing device as defined in claim 1 in which each of said stop members comprises a radially yieldable stop ring of resilient material having one peripheral edge disposed between and axially engageable with said abutments and an opposite peripheral edge which, by virtue of the radial resiliency of the ring, grips an opposed peripheral surface to provide a predetermined friction gripping force resisting displacement of the stop ring relative to and along the axis of said second magnetic ring.
 7. A torque-producing coupling as defined in claim 1 in which the torque resulting from gripping engagement of said magnetic rings, when the latter are energized, is transmitted solely through endwise stressing of said leaf springs and said second ring is supported at all times for free sliding of said pins within The surrounding walls of said holes.
 8. A torque-producing coupling as defined in claim 1 in which each of said stop members is a ring of resilient material and said abutments are the opposed walls of an annular groove surrounding the pins and wider than the stop ring by the desired width of said constant gap when the coupling is released.
 9. A torque-producing device as defined in claim 8 in which said groove is formed in said support as a slot opening outwardly in a plane normal to the coupling axis so as to permit of edgewise insertion of the ring into the slot and to a position of alignment with the axis of the pin hole.
 10. A torque-producing coupling as defined in claim 9 in which the free ends of said pins are frustoconical to facilitate projection of the pins through said stop rings after edgewise insertion of such rings in said slots.
 11. A torque-producing coupling as defined in claim 1 in which each of said stop members is a ring of resilient material expanded radially against the wall of the surrounding hole and the associated abutments are the opposed axially facing walls of an annular groove in the associated pin.
 12. In a friction coupling having relatively rotatable first and second rings of magnetic material adapted to be drawn into axial gripping engagement by magnetic flux threading a toroidal path through the rings, the combination of, a rotatable support, a plurality of leaf springs angularly spaced around and extending along secants of said first ring between said support and said ring, means securing opposite first and second ends of said springs to said support and the back of the ring respectively, said springs being stressed to flex laterally and to bias said first ring toward said support and away from said second ring upon deenergization of the rings, a plurality of angularly spaced pins rigid with said first ring adjacent said first spring ends and projecting parallel to the first spring axis, parallel holes in said support slidably receiving said pins, radially resilient stop rings encircling and slidable along said pins within said holes but frictionally gripping the pins to resist sliding along the pins with a force greater than said biasing force, and opposed axially facing abutments within each of said holes disposed on opposite sides of the ring therein and spaced apart to cooperate with the respective stop rings and limit axial separation of said first ring from the coacting magnetic ring so as to provide a gap of predetermined narrow width between the faces of said magnetic rings upon deenergization of the latter.
 13. In a magnetic friction clutch and brake of the character above described, a rotary hub, annular clutch armature concentric with the hub axis and disposed at one end of said hub, a set of leaf springs angularly spaced around and extending along secants of said armature between the latter and said hub, an annular brake armature disposed opposite the other end of said hub, a second set of leaf springs angularly spaced around and extending along secants of the brake armature between the latter and said hub, the first and second leaf springs being staggered relative to each other around said armatures and hub with one end of each spring of one set overlapping an end of the corresponding spring of the second set, rivets each extending through said hub and one pair of said overlapping spring ends and securing the latter to the hub, second rivets securing the other ends of said first springs to the back of the clutch armature, first parallel pins rigid with and constituting extensions of said second rivets and projecting rigidly from such armature and into parallel holes in said hub, third rivets securing the other ends of said second springs to the back of said brake armature, second parallel pins rigid with and constituting extensions of said third rivets and projecting rigidly from such armature and into parallel holes in said hub, one of said first pins and one of said second pins being angularly spaced apart wIth one of said first rivets disposed between such pins.
 14. A magnetic armature ring mounting as defined in claim 13 in which the pins of the brake and clutch armatures project past each other and the holes receiving such pins are disposed approximately in a common plane of said hub. 